Geographic Range

Corvus frugilegus is found in the Palearctic region, across much of Europe and Asia. Two subspecies of rooks are recognized: C. f. frugilegus and C. f. pastinator. The geographic range of C. f. frugilegus extends from Ireland eastward across Europe into Russia, with southern boundaries as far as Turkey and Iran. Sporadic, localized populations can be found as far north as southern Sweden, Norway, and Denmark. Populations have also been introduced in New Zealand, where they flourish. During breeding and migration, C. f. frugilegus can be found in northern Russia and the Mediterranean area, respectively. The geographic range of C. f. pastinator, commonly known as the Oriental rook, extends from eastern Asia west into northern Mongolia. The two subspecies are generally geographically separated by the Altai Mountains. (Madge and Burn, 1994)

Habitat

Rooks are widely distributed across Europe and western Asia, preferring arable land, river plains, and steppe regions where soil is generally soft and fertile. In agricultural landscapes, rooks tend to avoid areas where winter cereal grains such as rye and wheat are grown, instead preferring areas in which softer and more easily-accessible spring cereals such as barley are grown. Spring cereals are an ideal food source for C. frugilegus due to easy foraging that results from their small height. River plains and steppe regions also serve as excellent habitats for rooks because their rich soil is usually teeming with insects, and soft ground makes foraging possible. Rooks can also be found in areas bordering cities and towns as long as large trees are available for cover and food is available for scavenging. Given their wide occupation of much of Europe and Asia, rooks are able to tolerate a large elevation range, from sea level to approximately 4000 m. (Feare, 1974; Griffin and Thomas, 2000; Madge and Burn, 1994)

Physical Description

Corvus frugilegus is similar in appearance to C. corone (carrion crow), another species of corvid. Though both species are covered in glossy black feathers with a metallic sheen, rooks are distinguishable from carrion crows by their slightly smaller size, distinct wedge-shape tail, light colored bill, and prominently-fingered wingtips. Rooks average 47 cm long and weigh 337 to 531 g, but are considered large when compared to most other corvid species. Rooks show weak sexual dimorphism, with males slightly larger than females. In rooks, wing length ranges from 290 to 330 mm (wingspan ranges from 81 to 94 cm) and tarsus length ranges from 52 to 58 mm. For their size, rooks have a relatively large bill (53 to 57 mm long) that tapers to a sharp point. This long, sharp bill aids in food retrieval and eating insects. (Madge and Burn, 1994; Mullarney, et al., 1999)

Corvus frugilegus frugilegus tends to have a longer, thicker beak than that of C. f. pastinator, as well as a larger area of bare skin covering the forehead, lores (skin between eye and bill on side of head), and gular area (skin that joins lower mandible to neck). Corvus frugilegus frugilegus also has a violet sheen to its black feathers, whereas C. f. pastinator has a greenish sheen. Juveniles of both subspecies are easily recognizable by their brown-toned feathers and fully-feathered face, which does not become bare until their first spring. (Madge and Burn, 1994)

Reproduction

Despite their highly social nature, rooks form pair bonds that lasts from several years to life. Rooks generally take mates when they are two years old. During the fall mating season, pair bonds nest together in communal roosts called rookeries until they return to individual nests to lay eggs. Despite hundreds of birds in a single rookery, rooks maintain their pair bonds through extensive communication. Though rooks are known for being monogamous, like other corvid species such as Corvus corax (common ravens) and C. corone (carrion crows), there have been reported instances of bigamy and occupation of a nest by multiple females. (Green, 1982; Madge and Burn, 1994; Roskaft and Espmark, 1982; Røskaft, 1983)

Breeding and egg-laying usually begins around late February in Britain, but may be as late as April and May in central Europe and Russia where cold weather persists for a longer period of time. Rooks generally build nests in tall deciduous trees, though nests on the ground and in bushes are not uncommon. Nests consist of sticks and branches with a deep leaf, grass, and moss-lined cup. Rooks (Corvus frugilegus) lay two to seven (average four) blue-green eggs that are covered with brown and grey mottling. Rook eggs are very similar in appearance to those of ravens (C. corax), though slightly smaller, on average 40 mm long. After 16 to 18 days of incubation mainly by the female, the young hatch blind and helpless. (Kasprzykowski, 2007; Madge and Burn, 1994)

Breeding occurs in February through May, depending on length of winter.

Range eggs per season

2 to 7

Average eggs per season

4

Range time to hatching

16 to 18 days

Range fledging age

32 to 33 days

Average age at sexual or reproductive maturity (female)

2 years

Average age at sexual or reproductive maturity (male)

2 years

For the 16 to 18 day incubation period the female rook covers the eggs unless she has to briefly leave the nest, in which case the male takes over this duty. After hatching, the female tends to the young exclusively while the male delivers food. This continues for approximately the first ten days until the young become more self-sufficient, at which point the female joins the male in food gathering. At around 32 to 33 days old the young rooks fledge and leave the nest, but roost in nearby trees to remain close to the parents. The young continue their relationship with the parents for several weeks until they become fully independent. Even after reaching full maturity and independence, rooks generally remain members of their original rookery. (Madge and Burn, 1994)

Lifespan/Longevity

Not much is recorded on the lifespan of C. frugilegus, but like most Corvidae species, the rook is expected to live 15 to 20 years in the wild. According to the EURING European Longevity Records, the oldest rook found in the wild lived to be 22 years old. As is the trend, rooks in captivity may live for much longer. In a similar species, Corvus corax, the longest lifespan was recorded at 69 years for life in captivity. (Flower, 1938; Fransson, et al., 2010)

Average lifespanStatus: wild

22 years

Typical lifespanStatus: wild

15 to 20 years

Behavior

Rooks are highly social, living and interacting in large groups, although mating tends to monogamous. This bird species is largely arboreal and actively defends its territory. Rooks are active primarily during the day.

Communication and Perception

Rooks have a distinct call that has been described as sounding like a “caw." When rooks are defending or establishing a territory, multiple “caws” are used. Rooks also have a snarling call, as well as a gull call, which are used when an intruder comes within a short distance of their nest. In order to remain in contact with other rooks, a single loud “caw” is used during both foraging and migration. However, it is believed that rooks mainly vocalize with their mate, rather than in other social interactions. Like other birds, rooks perform singing duets (usually with a mate) that are believed to create a stronger mating bond. Female rooks use frequent vocalizations, by means of a begging call, in order to establish a submissive state with their mate, as well as to show dependency towards the male. Rooks also rely heavily on vocal communication with their young during the first few days of hatching. (Roskaft and Espmark, 1982)

Auditory communication is vital to the rook. They have a sense of hearing which helps them distinguish amongst other populations and species. The rook is able to recognize the call of a mate or its young. In addition to vocalizations, rooks also rely on visual communication, which becomes increasingly more important once young are able to open their eyes. Pecking is another form of communication, when an intruder rook comes too close to a territory; pecking attacks can occur usually resulting in the retreat of the intruder. (Roskaft and Espmark, 1982)

Food Habits

Rooks are opportunistic feeders. As omnivores, they eat any edible food item. Due to the strength and size of the bill, rooks are often found probing the ground in search of earthworms or other insects. Rooks also ingest small acorns, small fruits, and cereal grains. When the opportunity arises, rooks prey on small mammals, small birds, carrion, and eggs of the same species. They also have been known to act as “nest predators”, attacking the nests of other species of birds in order to eat the hatchlings and eggs. (Baughman, 2003; Bird and Emery, 2008; Feare, et al., 1974; Harrison, 1978)

Rook feeding habits often vary due to the location of their nest. Unlike those occurring in natural areas as above, those that live near urban sites also act as scavengers and take advantage of trashcans as well as abandoned food. Most rooks spend much of their time foraging at dawn and dusk. Primarily searching at dawn, rooks will pick through garbage bags to obtain food. However, they have been seen foraging during the day. Like all corvids, rooks store their food. (Baughman, 2003; Bird and Emery, 2008; Feare, et al., 1974; Harrison, 1978)

Predation

Little is known about predators of rooks. However, they appear to have similar predators to Corvus corax or Corvus brachyrhynchos, both similar and closely related species in the Family Corvidae. Owls, such as Bubo virginianus, hawks, or even intruding species of Corvidae tend to be the primary predators of rooks. Raptorial bird species prey on fledglings from nests more often than attacking adults. Humans may also pose as a threat to some species due to increasing tolerance of human presence. Humans are a threat due to shootings and habitat destruction of rooks. (Baughman, 2003; Harrison, 1978)

Ecosystem Roles

Rooks have numerous roles in the ecosystem. They serve as hosts for numerous protozoan organisms such as trypanosomes and leucocytozoans. Such organisms are generally not pathogenic and merely occupy rooks as vectors. While rook hosting of these organisms does not directly cause it any harm, it makes infection of other species possible. In this way, rooks sustain the lifecycle of these organisms. (Baker, 1974)

Rooks also serve as hosts for oribatid mites, among other types of mites. Oribatid mites are soil mites, and feed on dead plant and fungal material. These mites live in the feathers of rooks, where it is believed they consume fungi. Such a relationship does not harm rooks, it is actually beneficial, though its results are not readily noticeable. (Krivolutsky and Lebedeva, 2004)

Lastly, rooks play a key role in seed dispersal as they crack open and consume cereal grains such as barley. Without birds and small animals to crack open seeds and remove them from the plant, seed dispersal for cereal grains could be problematic or less efficient. (Lockie, 1956)

Economic Importance for Humans: Positive

While many farmers claim that C. frugilegus does more harm than good, recent studies suggest that 60 to 90% of insects consumed by rooks are agricultural pests. If this is the case, large numbers of rooks may have some impact on pest insect populations. Rooks are also known to dig into the soil in search of insects, so this may have a slight aeration effect which is particularly important in agricultural environments. Lastly, rooks play an important role in seed dispersal as they consume and crack open cereal grains. (Feare, 1974; Lockie, 1956)

Positive Impacts

controls pest population

Economic Importance for Humans: Negative

Rooks are commonly referred to as "agricultural pests", meaning they cause the loss and destruction of commercial crops. When foraging for food, rooks are often found in farmland crops, taking advantage of the cereals and grains. This can lead to an economic decline for farmers, as well as any person or company that may use the farmer for food. However, rooks are only known to cause damage to crops if the preferred food is not available. (Feare, 1978)

As well as being agricultural pests, rooks that live in urban areas are likely to get into garbage and rip open the bags, which can in turn cause problems for humans. (Feare, 1978)

Negative Impacts

crop pest

Conservation Status

Corvus frugilegus is classified as a species of least concern on the IUCN's Red List of Threatened Species. Corvus frugilegus is abundant and is able to maintain stable populations in its habitat. (BirdLife International, 2011)

Glossary

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

cooperative breeder

helpers provide assistance in raising young that are not their own

diurnal

active during the day, 2. lasting for one day.

duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

insectivore

An animal that eats mainly insects or spiders.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polarized light

light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

soil aeration

digs and breaks up soil so air and water can get in

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Baker, J. 1974. Protozoan parasites of the blood of British wild birds and mammals. Journal of Zoology: Proceedings of the Zoological Society of London, 172: 169-190.

Baughman, M. 2003. Reference Atlas to the Birds of North America. Washington, D.C: National Geographic Society.

Griffin, L., C. Thomas. 2000. The spatial distribution and size of rook (Corvus frugilegus) breeding colonies is affected by both the distribution of foraging habitat and by intercolony competition. Proceedings of the Royal Society of London, Series B, 267: 1463-1467.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.